#include<stdio.h>
int main() {
    long long factorial = 1;
    if(scanf("%d",&n) != 1) {
        printf("Invalid Input");
        return 1;
    }
    if(n < 0) {
        printf("Invalid Input");
    } else {
        for(int i = 1; i <= n; ++i) {
            factorial *= i;
        }
        printf("%lld\n",factorial);
    }
    return 0;
}